Conventionally, an object may be scanned by projecting a pulse light at the object. A reflected light from the scanned object is received to obtain information regarding the scanned object, such as a distance to the object, a relative speed of the object and the like. Coaxial type optical radar devices are examples of such optical radar devices, which have a light emitter and a light receiver coaxially disposed on the same axis.
Generally, coaxial type optical radar devices suffer from stray light (i.e., clutter or undesired-reflection light) generated inside or within a close proximity of the device. The stray light or clutter may enter the device and be received by a light receiving element. As a result, the stray light may be perceived as noise. That is, noise may be caused by the stray light. Consequently, patent documents 1 and 2 (i.e., Japanese Patent Laid-Open No. 3881313 gazette and JP-A-2008-232642), for example, disclose solutions for reducing the effects of stray light by desensitizing or reducing the sensitivity of the light receiving element during a period when stray light exists.
However, a consequence of desensitizing or reducing the sensitivity of the light receiving element during a period when stray light exists, is a disabling of the detection of the reflected light from the detection object itself. In other words, if reflected light from the object is received at the same time as stray light, due to the desensitizing or reduction of the sensitivity of the light receiving element, the light receiving element may not detect the reflected light from the detection object itself.